This paper presents the design and preliminary evaluation of an Accessible Digital Musical Instrument (ADMI) in the form of a tangible wooden step sequencer that uses photoresistors and wooden blocks to trigger musical events. Furthermore, the paper presents a short overview of design criteria for ADMIs based on literature and first insights of an ongoing qualitative interview study with German Special Educational Needs (SEN) teachers conducted by the first author. The preliminary evaluation is realized by a reflection on the mentioned criteria. The instrument was designed as a starting point for a participatory design process in music education settings. The software is programmed in Pure Data and running on a Raspberry Pi computer that fits inside the body of the instrument. While most similar developments focus on professional performance and complex interactions, LoopBlocks focuses on accessibility and Special Educational Needs settings. The main goal is to reduce the cognitive load needed to play music by providing a clear and constrained interaction, thus reducing intellectual and technical barriers to active music making.