differentiating for algebra II

my algebra II class has an interesting mix of students. 5 girls are getting solid A's or very high A's in the class, one has a B+, one has a B-, and two are currently getting Fs. after the recent test, i'm going to really encourage the people who got A's to try doing one of the available projects instead of doing the review parts of each homework assignment. i'm also going to add 4 problems or so to each homework assignment that the people who got A's on the test must try. i feel like the people who are getting As in the class aren't being challenged enough, and i would like them to be challenged, not bored (as i know a few of them are).