Project managers regularly allocate human resources to construction projects. This critical task is usually executed by fulfilling the minimum project staffing requirements, normally based around the quantity and competence of project members. However, research has shown that team performance can increase by up to 10% and 18%, respectively, as a consequence of the group members' heterogeneity and social cohesion. There is currently no practical quantitative tool that incorporates these aspects, allowing project managers to achieve this task efficiently and objectively. A new quantitative model for the effective allocation of human resources to multiple projects, which takes group heterogeneity and social cohesion into account, is proposed. This model is easy to build, update, and use in real project environments with the use of a spreadsheet and a basic optimization engine (e.g.,Excel Solver). A case study is proposed and solved with a genetic algorithm to illustrate the implementation of the model. Finally, a validation example is provided to exemplify how group heterogeneity and social cohesion condition academic achievement in an academic setting.