Aim/Purpose: This work aims to introduce and evaluate an instructional strategy that aids end-users with developing their software products during intensive project-based events. Background: End-users produce software in the labor market, and one of the challenges for End-User Software Engineering (EUSE) is the need to create functional software products without a formal education in software development. Methodology: In this work, we present an instructional strategy to expose end-users to Agile-based Software Engineering (SE) practices and enhance their ability to developing high-quality software. Moreover, we introduce a SE approach for the collection of metrics to assess the effectiveness of the instructional strategy. We conducted two case studies to validate the effectiveness of our strategy; the comprehensive analysis of the outcome products evaluates the strategy and demonstrates how to interpret the collected metrics. Contribution: This work contributes to the research and practitioner body of knowledge by leveraging SE centric concepts to design an instructional strategy to lay the foundations of SE competencies in inexperienced developers. This work presents an instructional strategy to develop SE competencies through an intensive and time-bound structure that may be replicated. Moreover, the present work introduces a framework to evaluate these competencies from a product-centric approach, specialized for non-professional individuals. Finally, the framework contributes to understanding how to assess software quality when the software product is written in non-conventional, introductory programming languages. Findings: The results show the effectiveness of our instructional strategy: teams were successful in constructing a working software product. However, participants did not display a good command of source code order and structure. Recommendations for Practitioners: Our instructional strategy provides practitioners with a framework to lay foundations in SE competencies during intensive project-based events. Based on the results of our case studies, we provide a set of recommendations for educational practice. Recommendation for Researchers: We propose an assessment framework to analyze the effectiveness of the instructional strategy from a SE perspective. This analysis provides an overall picture of the participants' performance; other researchers could use our framework to evaluate the effectiveness of their activities, which would contribute to increasing the possibility of comparing the effectiveness of different instructional strategies. Impact on Society: Given the number of end-user developers who create software products without a formal SE training, several professional and educational contexts can benefit from our proposed instructional strategy and assessment framework. Future Research: Further research can focus on improving the assessment framework by including both process and product metrics to shed light on the effectiveness of the instructional strategies.