Answer: I think that's fine as one approach to use.
An option that I would also use and would generally prioritize would be barbell push-ups. To do this, place a bar on the pins (safety bars) of the power rack and braced against the uprights. Have your trainee perform push-ups against the elevated barbell. The barbell can be set at various heights simply by adjusting the height of the pins. The lower the pins are set the more difficult the exercise.
The benefit of doing barbell push-ups instead of doing push-ups to a block under the chest is that they will allow a greater range of motion while still allowing the difficulty to be adapted to your trainee's current abilities.