Peer assessment was one of the most effective strategies to improve students' understanding, metacognitive skills, and social interaction. An online tool, "Designing for Learning and Portfolio (D4L+P)", was developed solely to support the T5 (tasks, tools, tutorials, topicresources, and teamwork) method of teaching and learning. This research used the D4L+P program ina project-based learning (PBL) approach and developed a marking scheme rubric as a topic resource in a task to improve peers' abilities as assessors. The objectives of this research were to compare the points offered for effort to plan proposals for science projects and the points offered for effort to give feedback, and also to analyze students' reflections as evaluators of the science projects using the D4L+P program compared to the reflections of teachers and experts in PBL. The participants were twenty-five grade 10 students aged 15 and 16 in a science enrichment program, 15 teachers, and five experts Findings showed that 94% of students preferred giving suggestive feedback about doing science projects. Results also indicated that the students and the experts had similar patterns of giving feedback (suggestive-corrective-reinforcing) while the teachers' patterns emphasized reinforcing feedback. The researchers regard the use of the D4L+P program with the marking scheme rubric in a PBL approach as an alternative learning strategy that requires students to practice the giving of suggestive feedback online.