Mechanism:

 Because the enolate ion is the chosen resonance structure, a better mechanism for the acid base reaction depicts the enolate ion being created at the same time like the acidic proton is lost. Since the hydroxide ion creates its bond to the acidic proton, the C-H bond breaks, and the electrons within that bond form a π bond to the carbonyl carbon atom. At the same time, the carbonyl π bond breaks like that both electrons move onto the oxygen.

Note: it is the electronegative oxygen which is responsible for making α proton acidic.