Young woodwind players often have trouble playing elegant, well-controlled accents. Accented notes are too often thumpy and out of tune. The most common manifestations are accented notes that are too flat, or that scoop up to pitch.
This is usually a side effect of the mistaken idea that accented notes should be tongued “harder.” The underlying misconception here is that the tongue “strikes” the reed in some way to kickstart its vibration. But the tongue merely releases the air that does the real work of starting the note, and releasing the air… harder?… doesn’t make a lot of sense.
In a misguided attempt to tongue harder, less-experienced players end up moving more of the tongue than is necessary. In good woodwind playing, the tongue serves at least two separate functions: the tip of the tongue releases the reed/air for articulation effects, and the back of the tongue controls the space in the oral cavity for voicing. Tonguing “harder” often involves the back of the tongue in the articulation process, which means the voicing changes, and thus the pitch changes.
Solve this problem by teaching a correct conception of articulation. Treat accents as note shapes, a dynamic effect.