The research aimed to develop and evaluate teacher concepts and performances before and after training through coaching and mentoring procedures integrated with the 21st century instructional strategies of project-based learning, problem-based learning, and research-based learning. The subjects were 96 teachers teaching at schools under the jurisdiction of Si Sa Ket Primary Education Office 3, Si Sa Ket Province, Thailand, purposively selected from 11 schools with lower average scores of ordinary national educational test (ONET) than those of the national level. The results revealed the teachers gained better concepts since the posttest scores were significantly higher than those of the pretest at the .01 level. The teachers’ performances were at a level of pass with distinction, they satisfied with the training session at a higher level, and their composed lesson plans were at a fair level.