I recently read a systematic review article about the efficacy of strength training for individuals with CP.
Basically, after reviewing multiple studies, the authors conclude that:
1) there is evidence that supports weight lifting to increase strength in both children and adults with CP
2) there appears to be no increased spasticity with strength training
The evidence is not clear enough to form evidence based recommendations for strength training just yet. But the authors do advocate balance and coordination exercises in addition to strength training exercises in order to improve mobility and functional movement skills.
Here’s a link to the article: