Capacity building usually follows any initiative. This also applies to education especially after curriculum reforms. This is to equip teachers with enough skills that would make them align their practices to the news standards. The focus of this qualitative study was to articulate the sensemaking and practitioner research inquiry of the teachers on their scaffolded collaborative lesson planning as one of the components of their on-going professional development (PD). Data were obtained from the formal and informal reflections of the teacher study groups who collaboratively worked on an inquiry-based lesson for elementary school classes. These data were audio and video-recorded, transcribed in verbatim and iteratively analyzed using the constant comparison method of the grounded theory. A priori codes from literature and the objectives of the PD program were merged with the data-driven codes to form the themes which established the findings on how the teachers as practitioner researchers made sense of their collaborative lesson planning experience and its implications to their professional identity. Final codebook were created, validated by an outside expert, and was used to code the anonymized transcripts. Results showed that three themes emerged which represented the teachers' sensemaking of their scaffolded collaborative PD: (1) cognitive and social process of adult learning; (2) collective ownership of learning resulting to professional commitment; and (3) research-based experiential learning. It was also found out that their scaffolded collaborative lesson planning experience created impact on their teaching profession as they articulated the activity as a venue for: (1) mutual leadership leading to increased feeling of effectiveness; and (2) improved teacher professional identity.