The Tauranga teenager originally sentenced to 20 months' jail for setting fire to the Life Education mobile classroom will now serve seven months on home detention.

Zachary Lance Fitzpatrick, 17, was sentenced in September after earlier pleading guilty to the arson of the mobile classroom worth $225,000 parked at Brookfield Primary School.

Zachary Fitzpatrick set fire to the $225,000 classroom earlier this year.

Fitzpatrick appeared in the Tauranga District Court today where he applied to have his jail sentenced substituted for home detention.

Judge Louis Bidois granted Fitzpatrick's application and sentenced the teenager to seven months home detention.

Fitzpatrick was also ordered to complete 120 hours community work.

On June 13 the teenager, who had been drinking during the day, entered the school grounds and smashed the window of the mobile trailer parked on the school's sports courts.

Inside he set fire to the curtains before fleeing through the back door.

Firefighters were called to the school where they found the trailer ablaze.

A short time later police arrived and found Fitzpatrick standing in a field nearby.

The trailer full of teaching equipment and audio visual items was completely destroyed in the blaze.

The Life Education Trust is a charitable organisation that visits Bay of Plenty primary schools helping students gain the knowledge to make informed choices.

Read more about the blaze here.