Recently, there has been increasing expectations for forest education to promote a sustainable society. Evaluations for forest education programs are needed, but there are few studies on internal evaluation methods for field educators to improve their programs. As a case study, we attempted to develop a simple method for measuring the effectiveness of a program that educators can use based on the Logic Model, employing the "Yamanoko" forest education project implemented by Shiga Prefecture. To make this method practical for educators, most of the work was done in collaboration with the authors and the field educators. First, we identified evaluation indicators (EI), categorized and quantified words that appeared in children’s reflections, and performed quantitative measurements of the program’s effects (Method I). Using this method, we compared the differences of EI scores between schools. Furthermore, we improved the convenience of the method (Method Ⅱ) by extracting only the "words" corresponding to EI from the impressions after experiencing the "Yamanoko" project. The results of Method I revealed that differences of the scores between schools were reflected in the interactions between children and educators. While we showed both methods can measure the program’s effects, we found Method II had a higher score of "impression / surprise" than Method I. In the future, it will be necessary to accumulate more data and examine whether the criteria for measuring effectiveness and the methods for classifying sentences and words are appropriate, to ensure higher validity and reliability.