The concept of self-directedness is a missing link in South African science classrooms, and as a result, science teachers are often not self-directed in employing innovative teaching and learning strategies such as blended problem-based learning (BPBL) that might enhance self-directed learning. The literature is replete with studies showing that science teachers in the United States, Indonesia, and South Africa, to name a few, lack the necessary technological skills to utilize simulations in the teaching and learning of physical sciences. This intervention-based explanatory mixed methods study was conducted in one of the nine education provinces of South Africa. Quantitative data were generated using a self-directed learning instrument (SDLI), the Physics Education Technology interactive simulations questionnaire, and a PBL questionnaire. Forty participants were sampled using both cluster and systematic random sampling techniques. Qualitative data were generated through a BPBL scenario, a reflective portfolio, and semi-structured interviews with two purposively selected participants. The quantitative data were analyzed using descriptive and parametric statistics. The reflective portfolio was analyzed using performance standards scoring rubric adopted from Smith et al. (2001). The BPBL Scenario Evaluation Schedule and interviews were analyzed using Saldaña's (2013) code-to-theory analytical model. It was concluded that there was a significant difference in participants' perceptions of PBL, self-directedness, and interactive simulations after attending a teacher professional development intervention (TPDI) and implementing BPBL. The findings show that the utilization of interactive simulations and PBL in physical sciences classrooms was unknown to teachers -- suggesting that teachers were not self-directed in implementing BPBL. This study presents a model for designing BPBL activities and an evaluation schedule for assessing those activities for self-directedness in educational practices.