During the relationship between May 2012 and November 2012, the girl was encouraged to deceive her parents, take time off school and lie to other students.
She left school and moved in with the teacher, who resigned his position at the same time.
The tribunal said it was "perhaps most troubling of all" that her schooling was cut short as a result of the relationship.
Tribunal chairman Kenneth Johnston said deregistration was the only realistic option. The teacher was also censured.
In the other decision, an experienced teacher sent "sexually suggestive" text messages to a year 9 boy, "goading the student into increasingly revealing information".
The teacher had been asked to help the student, who he had taught in the past, because the boys parents' were concerned about his academic progress.
However, one night "events took a different turn", the tribunal's decision read.
"The student had gone to bed and his mother was troubled because she heard series of messages being received by his cell-phone.
"She wanted to check who was texting her son so late in the evening, and in doing so discovered a number of texts between the respondent and the student sent and received over the previous 48 hours or so."
The boy's mother reported the texts to police, who investigated but did not lay any charges.
The investigation revealed 165 texts were sent over a three-week period, including 123 over two days.
They included invitations to text about "naughtier stuff" and frequent references to being in bed.
The tribunal's decision said they could not discharge their responsibilities to the public without ensuring the teacher did not teach in New Zealand schools for the time being.
The teacher was censured and deregistered. He would be able to apply for re-registration in the future, but at that time the Teachers Council would reassess whether he had overcome "whatever difficulties resulted in his behaviour".
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Excerpt from the text exchange:
Teacher: Yeah now I'm in bed if you want to text on naughty stuff? Only if you want to...
Student: No.
Teacher: Ok. I hope I did not upset you by asking that...
Student: No
Teacher: Cool. You like the idea but another time...?
Student: Yeah
Teacher: Ok. You like the idea quite a lot....? Lol
Student: No
apnz bm hm