Aim: To investigate whether speech therapy using a speech systems approach to controlling breath support, phonation, and speech rate can increase the speech intelligibility of children with dysarthria and cerebral palsy (CP). Method: Sixteen children with dysarthria and CP participated in a modified time series design. Group characteristics were as follows: seven males, nine females; age range 12 to 18 years (mean 14y, SD 2); CP type: nine spastic, two dyskinetic, four mixed, one Worster-Drought; Gross Motor Function Classification System levels range I to V (median IV). Children received three 30- to 45-minute sessions of individual therapy per week for 6 weeks. Intelligibility in single words and connected speech was compared across four points: 1 week and 6 weeks before therapy, and 1 week and 6 weeks after its completion. Three familiar listeners and three unfamiliar listeners scored each recording. Mean percentage intelligibility was compared using general linear modelling techniques. Results: After treatment, familiar listeners understood 14.7% more single words and 12.1% more words in connected speech. Unfamiliar listeners understood 15% more single words and 15.9% more words in connected speech after therapy. Interpretation: Therapy was associated with increases in speech intelligibility. Effects of the therapy should be investigated further, in an exploratory trial with younger children and in a randomized controlled trial.