Two studies were conducted to investigate the effect of a task-specific self-instruction intervention to improve handwriting ability of children with poor handwriting quality in schools for regular education (Study 1) and children with poor handwriting quality in schools for special education (Study 2). Study 1 showed that children with poor handwriting quality who received handwriting intervention on an individual basis for three months improved on average more on quality of writing than control children without handwriting problems who did not receive intervention. In contrast, the control group improved more in speed of writing after the intervention period. At an individual level, three out of the seven children with poor handwriting quality before intervention were not classified as such anymore after the intervention period. Study 2 showed that after six months of intervention in a group setting children with poor handwriting quality improved their quality of writing more so than children with poor handwriting quality who had not received intervention. On speed of handwriting no significant group differences emerged. We conclude that the task-oriented self-instruction method applied in this study seems to improve especially the quality of handwriting, not speed, of children initially identified as having poor handwriting quality.