This paper presents a prototype for an instrumented sorting block box designed for large-scale use in medical centers. A preliminary experiment was performed with unimpaired adults. Low-cost force sensors located under the top lid and realtime data processing allowed us to accurately estimate the position of the block. The data extracted from these sensors was used to develop and calculate suitable outcome measures such as the average distance to the target, overall time to complete the task, percentage of time spent far from the target, average force applied to the lid and number of mistrials. Results suggest a strong influence of the block shape, target location and movement number on the outcome measures. The tool and measures will be used for early assessment of abnormal development of motor skills in infants and for evaluation of pathological conditions such as cerebral palsy.