Elizabeth Carmichael, a married mother-of-two, was alleged to have had an affair with the teenager, who cannot be named for legal reasons, after they met at Kirkintilloch High School, East Dunbartonshire.
The 44-year-old, of Lenzie, appeared in private at Glasgow Sheriff Court in May last year charged with a sexual abuse of trust, but prosecutors have now dropped the case against her.
Her husband Alan, 53, supported her at court last year as she faced charges under Section 42 of the Sexual Offences (Scotland) Act, which states it is a crime to engage in sexual activity with someone aged 16 or 17 if you are in a position of trust.
A Crown Office spokeswoman confirmed proceedings against Mrs Carmichael had been dropped. She said: "After full and careful consideration of the facts and circumstances of the case, including all of the available evidence and the views of the complainer, Crown Counsel instructed that no further proceedings should be taken at this time.
"However, the Crown reserves the right to reconsider this matter should there be a material change in circumstances.
"The Crown has been in liaison with the victim in the case who has been advised of the position."
At the time of Mrs Carmichael's court appearance, East Dunbartonshire Council said it had launched its own internal investigation into the alleged affair.
The council has since confirmed the assistant, who also acted as a playground monitor, no longer works for the authority.
Director of community services at East Dunbartonshire Council John Simmons said: "It is against our policy to comment on former employees of East Dunbartonshire Council."
He refused to reveal whether Mrs Carmichael had been sacked or resigned.