In this study, the argument levels of pre-service elementary teachers (PSTs) were examined using The Predict- Observe-Explain (POE) experiments in the teaching of open-air pressure. The participants were 22 pre-service elementary teachers studying at a university in eastern Turkey. The study includes both the development of the worksheets and the application of worksheets. The researcher developed three POE worksheets. PSTs performed the experiments on the worksheets in a laboratory environment. The worksheets were analyzed according to the Toulmin argument rubric, which consists of claims, data, justifications, support, and rebuttals. In the study, PSTs initially struggled to make arguments, but as the application progressed, their ability to make arguments improved positively. Besides, PSTs have limited levels of high-level argument making.