Students with handwriting difficulties (HD) often show visual-motor challenges that affect sentence writing. However, few studies have compared the eye movements of HD and typically developing (TD) children when reading and writing. Recent studies have suggested that the proportion of time spent observing stimuli can help identify behavioral problems in children with developmental disabilities. This study compared the stimulus observation proportions between students with HD and TD peers. Japanese HD (n = 12) and TD participants (n = 15) were examined for differences in eye movement patterns when reading and writing Japanese sentences and compared reading and writing performance for meaningful and meaningless sentences. Eye movements were recorded while participants wrote several Japanese sentences. The results indicated that TD participants read and wrote sentences more fluently than HD peers, although no group differences were found for meaningful writing tasks. HD participants observed sentences more frequently in both reading and writing tasks than their TD peers and showed shorter observation spans and lower observation ratios during handwriting; however, their observation proportions during reading were comparable. Binary logistic regression revealed that letters per minute, the proportion of time spent on meaningless handwriting observations, and motor coordination scores were key indicators for identifying students with HD. These findings suggest that shorter observation spans and lower proportions of stimulus observation when writing reflect an HD student's tendency to merely glance at sentences rather than read them thoroughly.