Efforts were made to verify the effect of metacognitive scaffolding as an instructional strategy on learning outcomes related to concepts of acids, bases, and salts for ninth-grade pupils in physical science. A quasi-experimental pretest-posttest design was employed. One hundred and seven (107) students from two government-sponsored schools chosen using a purposive sampling technique in the city of Kolkata, West Bengal, India, were sampled. For the experiment, 55 learners in the experimental group and 52 in the control group were selected. Only the experimental group of learners received treatment via metacognitive scaffolding. To obtain data, the researcher administered a self-developed and standardised criteria test (with a reliability coefficient of 0.86 and a validity of 0.93) and a reaction scale. For data analysis, one-way ANCOVA, percentiles, means, standard deviations, and coefficients of variation were applied. Results of the study demonstrated that the students who received treatment acquired better learning outcomes than the others. Furthermore, treatment recipients responded favourably to the use of metacognitive scaffolding when learning physical science.