Somebody is going to be spending some money.
From the question, it seems that the school has not set up a lab environment for the course. Your purchase of Pis was a good move in the right direction. To be useful, your Computer Hardware and Software course needs to be more of a lab style course than a knowledge-based course such as history or math. Making it more hands-on for the students might even help reduce the rowdiness and tame the ADHD.
There is no age requirement, from CompTIA, for taking the tests. CompTIA does, however, recommend 13 as a likely minimum age. (A point to return to later.)
The overview from CompTIA provides:
Specifically, we recommend that you have the following skills and knowledge before starting this course:
- Recognize the main components of a PC and different data media such as USB drives and DVD.
- Start the computer and navigate the desktop.
- Use Windows Explorer to create directories and subdirectories and manage files.
- Use a web browser such as Internet Explorer to view websites.
After reading the CompTIA A+ 220-901 Certification Study Guide, you will be able to:
- Identify types and characteristics of PC, laptop, and mobile device components, including motherboard, CPU, memory, and storage, input, and output devices.
- Install, configure, and troubleshoot peripheral devices and system components.
- Install, configure, and troubleshoot print devices.
- Install, configure, and troubleshoot wired and wireless LAN links and Internet access devices.
After reading the CompTIA A+ 220-902 Certification Study Guide, you will be able to:
- Install, configure, and troubleshoot the Microsoft Windows, Linux, and OS X PC operating systems plus iOS, Android, and Windows mobile devices.
- Configure and manage PC and mobile device network connectivity plus users, groups, and shared resources in a typical SOHO network.
- Use anti-virus tools to prevent and recover from malware infections.
- Configure access control measures, such as authentication, security policy, encryption, and firewalls.
- Perform basic PC maintenance while working safely and responsibly and communicate effectively with customers.
Based on the test expectations, I would surmise that while you may not be well versed in each objective, you have a solid foundation of experience and exposure which will make gaining the requisite knowledge easier than you're anticipating. In practical terms, the level of knowledge being tested is mostly just a notch or two above "common knowledge" anyway. Reading the book by Mike Meyers (see next section) could be all you need to learn about the A+ to be able to teach it to your students. I'd still recommend getting a copy of the Official study guides anyway, even if you find a used one somewhere. The manner they present the information is influenced by how they will test for it, and knowing that will help you design your course to help ready your students for the test.
It seems a bit much to expect that high school students would be able, and willing, to purchase their own copy of the official CompTIA A+ Study Guide. As the instructor, however, you probably should. As an alternative, or supplement, you could read CompTIA A+ Certification All-in-One Exam Guide, Ninth Edition (Exams 220-901 & 220-902), by Mike Meyers. In various versions, his CompTIA related books have been recommended reading. This book is probably available in your local public library, or through ILL if they don't have it.
As a guide for developing your course you can at least review the objectives for the two A+ tests, (hardware) 220-901 and (software) 220-902. An extra problem is that the 220-901/220-902 test series is old. They were launched in Dec., 2015, and are set to be retired in July 2019. If a partial objective for the course is to prepare the students to pass the exams after the course, there could be a timeline issue. The current test is set to retire at about the same time as the students would be finished with the course.
The CompTIA tests are billed as "vendor-neutral" and they do cover the majority of the field, including Linux, Mac OS, iOS, and Android, in their testing. Windows is still the priority for the testing, with almost all the software and networking scenarios involving Windows-based tools for their solution. That said, without the exposure and practice with Linux, and the mobile OSes, they are unlikely to achieve a passing score on the real tests. What little there is for Android and iOS can be discussed and some of the students can practice on their personal phones, since it mostly involves increasing security or connecting to networks and email servers. The improved security on their devices will not be a bad thing at all.
While it is not, technically, required, the A+ preparation course will be most effective if it is based on in-lab experience more than memorization of material. (Think of automotive mechanics more than chemistry.) Especially in the hardware section (220-901), what the students need to learn is what they can do rather than know. The software test (220-902) is more evenly split between skills and knowledge. Even so, doing it will mean more than knowing it. This means having a "lab" available to practice in. The lab does not need to be anything permanent at all. One A+ Prep course that I was familiar with at a community college used a regular classroom. The instructor had all the elements needed stored in a collection of plastic crates and they were wheeled into the classroom on a hand truck for the class twice a week.
Build a test lab with a couple desktop computers with monitors, a couple network hubs and/or routers, cables that work (and some that don't :D) and extra hardware (HDD, RAM, printer, external devices including USB HDD). In this case cutting edge is not as good as old-school. An old Intel Pentium Dual Core/AMD Athlon 64 x2 with a motherboard that is just new enough to include a SATA port along the IDE port(s) and smallish HDDs, 150-300GB, in a mix of IDE and SATA. An extra advantage of using the older (ancient?) hardware is that you can probably find it very inexpensively in thrift shops and second hand stores. Since it is for school, you may even convince a local electronics recycling center to donate some of those parts. If you can amass sufficient spares you won't have to worry about the occasional damaged parts.
In addition, even a non-working notebook (laptop) which can be dissected, and a few samples of other portables to allow the students to see the internals, would be helpful. Opening a notebook computer can be tricky - usually there is one piece you have to "pry" off first, after which it becomes a puzzle box, removing screws and pieces in the proper order.
On the software side, specifically the OSes, you can get by with, and I recommend using, Windows XP Pro, and an older Linux more appropriate for the collected hardware. The "latest and greatest" Linux kernel will probably work on the suggested systems, yet newer kernels will not supply any additional benefits to the students, be larger, and take longer to install. A system that can be installed from a CD (not a DVD) and operate without updates or extra installed packages allows the students to practice setup and configuration of Linux without needing an Internet connection for the box each time. Likewise, with Windows XP Pro, Service Pack 2, you can do a complete install without having to access the Web for updates or drivers. As the system will be installed, and then removed, repeatedly, there is no issue with the licensing for Windows, and you will not have to perform activation. One legal CD-KEY is all you need. (Several copies of the install disk, however, is strongly advised.)
This probably the hardest part to give pointers on, as I have never met your students, and do not know anything about their background. The one point that seems to apply in almost any situation, however, is "self-interest." Other than the rare student who loves knowledge for its own sake, they are not going to be very motivated by "knowing" something unless it makes "getting" something easier. knowledge of why the students are in that class could help. If they took that course because the school/district/state requires it, the only "motivation" they start the course with is "pass the class." Worse, though likely, is that the course had a reputation as an "Easy A" with the prior instructor, and the current students selected your course to avoid doing any learning while collecting a needed elective credit for graduation.
As mentioned in the prior section, CompTIA has no age requirements for the A+ Certification. If the course has, or can be given, the objective of passing the CompTIA A+ Certification tests after completion, one possible motivation can be that your students, still "minors", can obtain a certification that is meant for adults, and having it might open doors for summer jobs, with good pay that even a lot of adults couldn't get. The exams themselves are not inexpensive, however. The CompTIA A+ Certification requires two tests, and they are $219 US each, with no refund for not passing. If the school was willing to fund, as a scholarship, the testing for students who get an 'A' in the course, that might provide an inducement as well.
The subject matter for your Computer Hardware and Software course is, by nature, dry. The sector layout of spinning rust just is not exciting. I like having my systems very personalized, yet I don't find reading about config settings the least bit entertaining. (I probably will not remember what the settings mean next week either.) Making something, and seeing your work produce results, can be quite fulfilling, however. If you are able to create the "lab" and the students can learn about the hardware by building a computer from scratch, there is the challenge of getting it done, and the thrill of seeing it come alive the first time when they get it right. The more "boxes" you have available for building, the better. Still, with just wo, you can make it into a team project, and the teams can take turns building a system. You can even create a pattern where one team builds part of the system, and another team finishes it without knowing what the first team did until the examine the partial build in person.
If the students truly are ADHD, as the question states, then the hands on approach will help even more. In addition, you can limit your "lecture" time to short segments inter-spaced with some form of kinesthetic learning. Something as simple as passing around an HDD to examine can break the lecture into manageable chunks, give the students an excuse to move their bodies, and help them associate something physical with whatever you've been saying. As a general beginning point, limit the time students have to pay attention to you to intervals of 20 minutes, or less. Allow, or encourage, moving about the room for a couple minutes between segments. Walking about the room, or other large motor movements often help with alertness and can improve focus during the other times.