Scratch comes with a large document of day-by-day lessons along with labs. As a side benefit, due to the exploratory nature of Scratch, creating new assignments is fairly simple. "Create a movie about ____" or "create a small game that involves bouncing" or "create a game that responds to sounds as the controls".
Actually, that blank is great. You can tell the students to create a "movie" or a game about any topic the kids are studying elsewhere in the curriculum, and allow them to make use of all of the techniques they've learned and explore other parts of the program.
To my thinking, it's also advantageous to use scratch concurrently with logo, since using two systems will introduce the key computer science concepts twice within two giant, open, exploratory worlds. This increases the chances that the kids will see the parallels and really begin to absorb the computer science concepts.