acclimatize

　DY（03/16/12付）のThe Language Connectionより英語表現を拾います。

A:At Little America, we separate students according to level, not age. We have five levels: beginners, intermediate, advanced, honors and international academic. Of course, most students in the beginner classes are younger students, and the majority of students in the high-level classes are older. But there are always exceptions to the rule. Students are eligible to graduate to the next class level four times a year. This is possible at our school because we have many students. In your case, two divisions work for you, but you are not sure what to do with the new first-graders.

I understand your dilemma because there is a big difference between a kindergarten class and a primary school class. I have noticed that it usually takes about three months for first-graders to acclimatize themselves to a new, structured setting and system, which requires more concentration, self-discipline and focus compared to the entertaining activities (such as singing and dancing) of kindergarten.
http://www.yomiuri.co.jp/dy/features/language/T120309003612.htm

　acclimatizeは「（人・動植物など）新風土[新環境]に慣らす[慣れる]，順化[順応]させる[する]，馴致する」とあります（『リーダーズ英和辞典』研究社）。確かに，acclimatizeにはac＋climat＋izeと分解すると，climateが隠れていることに気付きます。
　英和辞典には，acclimatizeとacclimateは同じ意味で載せられていますが，OEDをひくと，生物学の用語として使われると，意味が異なることがわかります。

acclimatize... respond physiologically or behaviourally to changes in a complex of environmental factors

acclimate... respond physiologically or behaviourally to changes in a single environmental factors

また，植物学の分野では，harden offという意味で，この場合は，acclimatizeもacclimateも意味は変わらないようです。
　acclimatizeやacclimateは，climateが隠れていることから，生物学や植物学，また生物の成長過程などの話題で出会うことがある単語だといえるのではないでしょうか。