Children begin to investigate angles formally.
They explain angles in 2 ways – as the relative slant of 2 arms that meet at a vertex, and as the amount of turn around a vertex.
Children investigate a protractor, explaining that the number going in both directions allows us to measure angles in any orientation.
Children measure angles with a protractor, identifying right angles, straight angles, and revolutions, as well as acute angles, obtuse angles, and reflex angles.
While children are developing this understanding, they immediately investigate side and angle properties of shapes. (Measurement and Geometry 49).