Sentence:  Individual differences in <WSD>maturation</WSD> and the development of readiness for learning to read indicate that not until the third grade have most children had ample opportunity to demonstrate their capacity for school achievement . 
Meaning of the word marked with <WSD> tags:  (biology) the process of an individual organism growing organically; a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level