Working memory capacity (WMC) refers to the capacity of working memory, the ability to maintain, manipulate, and access mental representations as needed to support complex cognition. WMC varies widely across individuals and predicts higher-order cognitive abilities, which influence academic achievement in the domain of mathematics and science learning. If we understand the causal model of WMC, we can enhance the academic achievement. Currently, there is less study on Thai student's WMC. There were nine observed variables. Data were collected from 212 students, grade 7th - 12th, using Computerized Battery Test1 (CBT1) to measure recognition, attention and working memory while doing simple tasks, and using Computerized Battery Test2 (CBT2) to measure WMC. The data were analyzed by the M-Plus Statistical Modeling Program. The results showed that The causal model was fitted with the empirical data (x 2 =0.241, RMSEA= 0.03, CFI= 0.976, TLI= 0.963, SRMR= 0.048). The guide can be developing WMC of Thai children.