A growing number of primary school students experience difficulties with grapho-motor skills involved in handwriting, which impact both form and content of their texts. Therefore, it is important to assess and monitor handwriting skills in primary school via standardized tests and detect specific grapho-motor parameters (GMPs) which impact handwriting legibility. Multiple standardized tools are available to assess grapho-motor skills in primary school, yet little is known on between-test agreement, on impact of specific GMPs on children's overall performance and on which GMPs may be specifically hard to tackle for children that are starting to consolidate their handwriting skills. These data would be extremely relevant for clinicians, therapists and educators, who have to choose among different assessment tools as well as design tailored intervention strategies to reach adequate performance on different GMPs in cases of poor handwriting. To gain better understanding of currently available standardized tools, we compared overall performance of 39 Italian primary school children (19 second graders and 20 third graders) experiencing difficulties with handwriting on three standardized tests for grapho-motor skills assessment and explored the impact of individual GMPs on child performance. Results showed some agreement between tests considering all children in our sample, but no agreement in second grade and only limited agreement in third grade. Data also allowed highlighting significant correlations between some GMP scores and children's overall performance in our sample. Finally, children in our sample appeared to experience specific difficulties with some GMPs, such as letter joins and alignment.