Grades:

1st Grade ( Year 1)   |   一年生   |   ichi nen sei.
2nd Grade ( Year 2)   |   二年生   |   ni nen sei
3rd Grade ( Year 3)   |   三年生   |   san nen sei
more info: Classroom English / Classroom Japanese; ni nen sei ; Watashi wa NI NEN SEI DESU!

一年生 no Kanji
年 : nen : year (years)

1 nen sei no kanji

(1st Grade Kanji)

一          ichi             - one, the number one   

一番       ichi ban       - #1, the best	(see 番 / ban)

世界一    sei kai ichi    - the best in the world	

一人       hitori            - one person, alone

All the Kanji on the Japanese Language Proficiency Test Level 4
Same Site: includes Ichi Nen Sei Sanji

See also: Telling Time In Japanese