In my AB/BC stacked AP calculus class, I have a wiiiiiiiiidddddddeeeee range of abilities. The same holds true for my 2nd AB class. I've tried various things, but the "lower" end stays at the lower end. I just finished grading and handing back the latest test, and the "low" scores were still low. I'm talking about 4 kids out of 19 in one class and 6 out of 28 in the 2nd class. The others are fine. So I threw it back at the class and asked them to write suggestions on how to make sure EVERYONE understands every topic. I got great feedback.
Some student ideas:
* have study buddies in class. after a day or so of instruction, have a practice day where lower and higher students are paired up.
* don't teach the "tricky" stuff in class, just go over the basics so we get a good grasp.
* for homework, also include varying levels of difficulty from basic skills to AP level type questions.