"Sensitive window" replaced "critical period" because it suggests:

1. Research shows a range of ages linked to different language abilities. 2. This prompted a change in terminology from critical periods to sensitive windows. 3. Sensitive windows suggest optimal periods for learning, whereas critical periods suggest cut-offs. 4. So the new term stresses best times, not hard limits. **Why not the others:** A fixed cut-off is the meaning of "critical period". The term does not limit learning to adults or deny that age has any effect. _Source: NCERT, Position Paper of the National Focus Group on Teaching of English (2006), section "4.1 The critical period or sensitive window hypothesis", PDF p. 27 (ncert.nic.in/pdf/focus-group/english.pdf)_