(1) Any annexation which would have the effect of detaching part of the area of an existing school district shall not become effective prior to court approval as specified in this section; except that this subsection (1) shall not apply to an enclave area which has five hundred or less inhabitants nor to any annexation the petition for which is signed by one hundred percent of the landowners in the area proposed to be annexed.

(2) In the event of an annexation as set forth in subsection (1) of this section, the annexing municipality, within ten days following the election as provided in section 31-12-107 or the adoption of the ordinance as provided in section 31-12-106, shall give written notice of intention to annex, pursuant to this part 1, to the board of education of the school district from which it is proposed that the area will be detached.

(3) Within thirty days after the notice of annexation proceedings specified in subsection (2) of this section is delivered to the board of education, the annexing municipality shall petition the district court in accordance with the jurisdictional requirements set forth for review of the governing body's actions in section 31-12-116 (1) for the granting or denial of the requisite court approval to consummate annexation. The petition shall name the board of education as party defendant.

(4) The court shall determine:

(a) On the basis of the most recent assessment, the aggregate valuation for assessment of all property in the school district and the aggregate valuation for assessment of all property in the territory proposed to be annexed; and

(b) On the basis of the most recent enrollment records of the school district, the aggregate number of pupils enrolled in the school district and the aggregate number of pupils so enrolled who live in the area proposed to be annexed.

(5) If the pupil percentage (the percentage of all enrolled pupils that is reflected by all enrolled pupils living in the area proposed to be annexed, carried to four decimal places) is less than three-fifths of the property percentage (the percentage of aggregate valuation for assessment of all property that is reflected by property lying within the area proposed to be annexed), the court shall disapprove the proposed annexation, and such annexation shall not become effective; except that the court shall not be required to disapprove a proposed annexation if it finds that ninety percent of the aggregate valuation for assessment of property in the area to be annexed consists of unimproved land. In no event shall the court approve a proposed annexation which, together with the valuation for assessment of all other property detached from a school district in any one calendar year, exceeds five percent of the aggregate valuation for assessment of all property in the school district.