There is no guarantee, but experience indicates a one letter-grade improvement or better for almost every student that uses the videos, even those with special needs.  That performance expectation is not unreasonable when you consider some of the differences between classroom instruction and video instruction:

1. Video instruction can be repeated
2. Video instruction has no distractions
3. Video instruction is available at any time of day
4. Video instruction is available when the student is ill or on vacation