The aim of this study was not only to help pre-service English language teachers (PS-ELTs) to design vocabulary learning materials for a web-supported situated learning (SL) environment but also to have them learn the vocabulary they used to prepare those materials in the web-supported SL environment. Also, the effects of this process on the PS-ELTs' academic achievement, self-efficacy beliefs in designing situated learning environments (SEB-SLE), and technological pedagogical content knowledge self-confidence (TPACK-SC) were revealed. One of the advanced mixed-method designs, intervention design, was employed, and 56 PS-ELTs participated in the study. The data were collected via quantitative measurements (two scales, a vocabulary achievement test) and qualitative measurements (student diary, online messaging logs, open-ended interview form, and focus group interview records). For the quantitative data, independent samples t-test, related-samples t-test, and 2X3 repeated measures ANOVA test were used; for the qualitative data, content analysis. The results showed that there was a significant difference between the within-group gain scores and retention test scores in terms of the vocabulary achievement test and the SEB-SLE scale. However, despite a significant difference in the within-group gain scores in terms of the TPACK-SC scale, no significant difference was found between the post-test and retention test scores. Moreover, although both groups revealed no significant differences in the scores of the vocabulary achievement test and the TPACK-SC scale, the scores of the SEB-SLE scale showed a significant difference in favor of the treatment group. Related to the procedure, PS-ELTs highlighted that preparing vocabulary learning materials according to the web-supported SL model had a considerable effect on their vocabulary learning. Besides, the application process supported permanent learning and vocabulary knowledge development. What is more, the procedure helped them gain critical thinking, problem-solving, synthesis, and research skills as well as improving their TPACK.