Catherine Towey, 35, asked the infatuated fifth former if a dress she had worn was too skimpy and “low cut” and said kissing him would be “just lovely”.
She also said she loved him and wanted to “lie with him”, a professional conduct panel of the National College for Teaching and Leadership heard.
And they had a series of “personal and inappropriate meetings” in the evening before the relationship was exposed.
Ms Towey, who was assistant headteacher at The Elmgreen School in West Norwood, south east London, between September 2013 and January 6th last year, resigned after a sixth form student reported what was going on to a staff member.
That pupil provided screen shots from the work email account of Ms Towey containing messages between her and the boy, only identified as Pupil A.
They included a reference by Ms Towey to her “proper boobs”, offering to wear lipstick “more often” if Pupil A liked it and a discussion about whether a dress had been “too little and too low cut”.
His attention and personal interest in her looks, clothes and make-up boosted her ego after the break-up of a previous relationship.
In response to one or more expressions from “emotionally vulnerable” Pupil A that he wanted to kiss her she said she felt “properly close” to him and a kiss would be “weirdly natural and just lovely”.
Another reply expressed “me too” and stated “why d”ya think I”m always trying to hold your hand?”.
She stated “it”s not too ambitious to get a kiss by Christmas”, said “she might faint” if it ever happened and called Pupil A a “tease” after he said she wouldn”t know if his use of the word “love” was just a saying.
When Pupil A stated he likes girls “short and slim like Miss Towey” – with a wink emoticon – she replied “too cute!”.
She stated she “just want to lie” with Pupil A and “I heart you… maybe it”d be easier if I didn”t. But would I change that now? Simple… no. never. Can”t turn it off now.”
Ms Towey also described their relationship as a “shared crush”.
The panel found Ms Towey”s conduct was “sexually motivated” although it accepted she never wanted nor would have let the relationship “become physical”.
Michael Lesser, chair of the panel, said: “Ms Towey accepts the attention bestowed on her by Pupil A fed her ego.
“She was obviously revelling in the fact that he desired her and the sexual frisson that created between them.
“Her motivation in corresponding and meeting with him in the manner in which she did was designed to make herself feel desirable and attractive by playing on and encouraging Pupil A”s hopes of some physical consummation of the flirtation.”
Ms Towey was found guilty of unacceptable professional conduct and conduct that may bring the profession into disrepute.
Mr Lesser said: “The emails which were sent by her to Pupil A were manifestly inappropriate as were the pre-arranged meetings.”
Ms Towey was prohibited from teaching indefinitely and cannot teach in any school, sixth form college, relevant youth accommodation or children”s home in England.
Decision maker Mr Alan Meyrick, on behalf of Education Secretary Nicky Morgan, said she may apply for the order to be set aside in three years.