Elementary students who demonstrate accuracy and speed in handwriting are better equipped to generate higher quality, longer composition. Unfortunately, students with autism spectrum disorder (ASD) tend to encounter significant difficulties with legibility, size, and speed of handwriting. The present study used a single-subject, multiple-baseline design across participants to examine the effects of CASL (Center for Advancing Student Learning) Handwriting intervention on handwriting accuracy and speed for three early elementary students with ASD. The dependent variable was correct letter points (CLP) and error letter points (ELP) as measured on a 90-s sentence copy probe. The intervention was delivered over eighteen, 20-min sessions which included alphabetic knowledge activities, explicit instruction in handwriting, and timed practice with goal-setting, praise, performance feedback, and self-graphing. After starting intervention, all students showed immediate increases in overall handwriting accuracy. Throughout intervention, handwriting accuracy continued to improve for each student, and handwriting speed increased for 2 of 3 students. However, the observed gains fell short of high levels of accuracy needed to achieve fluency as a learning outcome. Results extend prior research on handwriting intervention for students with ASD, the CASL Handwriting Program, behavioral fluency theory, the Instructional Hierarchy, explicit instruction, and timed practice.