The scrapbook makes no mention of this ceremony, but presumably it was a secular version of the crowning of the Virgin Mary that traditionally take place in May in many Catholic schools. The date on the back of the photograph may be an error.
"Crowning the Cow," R.C. Davey School, 1926 [sic]. The students are Grace Kane, Rosalie Conterman, Borghil Biertsen, and Louise Gilpin.