N.H. Rev. Stat. Ann. § 189:19

In the instruction of children in all schools, including private schools, in reading, writing, spelling, arithmetic, grammar, geography, physiology, history, civil government, music, and drawing, the English language shall be used exclusively, both for the purposes of instruction therein and for purposes of general administration. Educational programs in the field of bilingual education shall be permitted under the provisions of this section with the approval of the state board of education and the local school district.