The document discusses using a digital tool to improve students' algebraic skills in the Netherlands. It describes three rounds of research involving over 300 students testing whether the tool could effectively develop both procedural skills and conceptual understanding. The tool included interactive exercises addressing common misconceptions with principles of providing feedback, addressing crises or errors, and gradually fading feedback. Post-test scores were significantly higher than pre-test scores, indicating the tool was effective. Higher post-test scores correlated with previous knowledge, time spent self-testing and on summative assessments, and general math attitude.