The performance of a fundamental motor skill in early childhood can be investigated using diverse assessment tools. Although the classical tests are reliable and useful for motor skills assessment, they have some limitations. The launch of the Microsoft Kinect marked a revolutionary advancement for developers thanks to the depth camera and its affordable price. This work aims to develop a reliable computer-based application using the Microsoft Kinect sensor to implement the third version of the Test of Gross Motor Development (TGMD-3). The assessment consists of customized algorithms that verify if the 3D position of the most relevant joints for each subtest varies along time according to the respective performance criteria. The proposed system returns an immediate feedback to the participant, indicating if s/he passes or fails the selected subtest. The results revealed the computer-based application for assessing gross motor skills is accurate, although it is limited by the space requirements.