A jury Wednesday convicted a middle school teacher on 35 felony charges stemming from a scheme to have students in his class undress so he could photograph them in sexually explicit poses in exchange for items, including a duck call.

Marshall Adam Walker, 33, was convicted on 30 counts of sexual exploitation of a child, three counts of unlawful sexual contact, and two counts of enticement of a child, district attorney spokeswoman Pam Russell said in a statement.

Walker developed relationships with three boys — ages 13, 14, and 15 at the time — while he was a student teacher at Bell Middle School in Golden in 1997 and at Everett Middle School in Wheat Ridge, where he taught from 1998 until his arrest in May, Russell said.

He met one of the boys at Bell and two others while at Everett.

Prosecutors said Walker would invite the boys to go hunting, shooting, movies and going out to eat. To get the boys to pose, he would offer them items such as a gun, pornographic videos, and in one case, change a failing grade, prosecutors said.

Walker, of Thornton, taught science, coached boys basketball and participated in hunting and fishing activities, sheriff's officials said.