Teen accused of killing mom and burying her in a fire pit after an argument over his D grade

A Florida teenager has been charged with first-degree premeditated murder after he allegedly strangled his mother to death and buried her in a church fire pit after an argument about his D grade, according to police.

The boy, 15, confessed to killing of his mother, Gail Cleavenger, 46, according to Volusia County Sheriff Mike Chitwood.

The teenager appeared in juvenile court on Sunday along with two 17-year-old co-defendants who were charged as accessories after the fact to first-degree premeditated murder.

It is not clear yet whether the teenagers will be charged as adults, and none of the defendants have entered any pleas.

The attack took place early Friday morning after Cleavenger called her husband -- the boy's stepfather -- who was on a business trip in Washington State, and informed him about her son’s D grade and the subsequent argument, according to police.

Asked at a previous press conference on Friday what motive would have prompted a matricide, Chitwood responded, "Rage."

“Apparently there was a dispute about [grading] marks with his mother, and after an argument that occurred around 11 o’clock, around 12:30 he went into her room and woke her up and began to strangle her until he killed her,” Chitwood told reporters at a press conference.

After strangling her with a rope, according to police, the son used wheelbarrow to move his mother's body to her truck and then drove it to River City Church and buried it in a fire pit.

The teen allegedly implicated two other friends whom he said helped him bury his mother and stage a burglary scene at his home. Then, police said, the teen returned home from school Friday and placed a call to 911 at 3:52 p.m., reporting a break-in.

Police also arrested his two friends, both 17. Both alleged accomplices remain in custody. While they have, too, have yet to be formally, charged, police said they are likely facing multiple criminal charges.

“These guys helped him bury his mother back here," Chitwood said. "They helped him stage a burglary, and they helped hide all the electronics that w[ere] stolen from the house."

When police arrived at his home they found the front door kicked in, the house ransacked and Cleavenger’s truck in the driveway with the engine running, according to a police statement posted on the department's Facebook page.

Investigators spent hours talking with the son, Chitwood said at the Saturday press conference.

“He believed he was the smartest person in the room and he continued to tell us his theories of what he believed and why: what happened to his mom and where we should be focusing our attention,” Chitwood said.

Eventually, officials said, the teen changed course, admitted to the murder, and walked investigators through his plot and its execution.

“She was a mom. She was a wife. She was a sister. By all accounts she was an amazing human being,” Chitwood said.

ABC News' Jason Volack contributed to this story.