The purposes of this study were 1) Study teachers authentic assessment, teachers comprehension of authentic assessment and teachers needs for authentic assessment development. 2) To create teachers development model. 3) Experiment of teachers development model. 4) Evaluate effectiveness of teachers development model. The research is divided into 4 periods. The first period comprises 900 sample primary school teachers in Sakhonnakhon province. The second comprises were 15 evaluation experts. The third comprises 32 sample teachers in small, medium and large primary schools. The fourth period comprises the same 32 sample teachers to gather survey data, meeting seminars to arrive at conclusion from survey, literature analysis and observations. Statistical analysis is performed to find percentage, means, median, inter-quartile range, standard deviation, dependent sample t-test, while qualitative data is subjected to content analysis. The results revealed that 1) 900 primary school teachers in Sakhonnakhon Province undertaking and comprehension of authentic assessment were at the medium level while the expectation was higher than reality at 0.01 significant level. 2) The model which revealed 4 relationships: prior development study, teachers development planning, teachers development implementation and teachers development evaluation. 3) Experiment of teachers development model to authentic assessment revealed that understanding, attitude and capability to carry out authentic assessment were all higher than before at 0.01 significant level. 4) Evaluation of effectiveness of teachers development model to authentic assessment by empowerment evaluation approach found the model have utility, feasibility, accuracy, propriety and high teachers' satisfaction.