This book scientifically discusses the concepts of progressive education as developed by Emmi Pikler and Maria Montessori in the area of free play. The goal is to present, compare and evaluate the respective guidelines for an ideal upbringing. The basic question is which details parents and educators have to pay attention to when it comes to free play in order to promote ideal child development, and which benefits such an education can have for the child. Based on a content analysis, the respective concepts for presenting the pedagogical assumptions will be introduced. Furthermore, the parallels and differences between Pikler’s and Montessori’s theories will be discussed, and in those assumptions that differ, scientific studies shall show which approach is more beneficial for the child. For this purpose, several empirical studies will be taken into account and summarized as well as compared in a literature review. This will allow the reader a comprehensive overview over type and procedure of the different studies, making the results easier to interpret. Furthermore, the book contains an overview about the design and organization of playgroups according to Pikler and Montessori, as well as a developmental/psychological contemplation of free play and biographical information about the two progressive educators.