Mark (21) wants to be a father in the fullest sense, but without affordable housing he has to be a part-time dad - earning money to support his child, living with his parents and seeing his child four or five times a week.

We hear stories of young fathers walking away from the teenage mothers of their children, but Mark is different. He gave up the opportunity of a year in Australia to remain at home, working full-time to support his seven-month-old daughter and assist her mother, Rachel (19), in parenting so that she can start third-level education in September. The couple are committed to each other, yet cannot live together because private rented accommodation is unaffordable. They're on the housing list, but know they will be waiting for years.

The result is that Rachel and the baby live between two homes - Rachel's mother's and Rachel's father's. Rachel's parents are separated and have new partners and other children from these unions. The baby also spends time at a third home with Mark's mother, who will care for the baby when Rachel returns to full-time education. When Rachel and her family go on holiday abroad this summer, Mark will give Rachel a break by using his own holiday time to care for the baby.

The prospect of Mark, Rachel and the baby having a holiday together is unthinkable for the couple, who have to save every cent in the hope of one day affording a private flat.

Every year, more than 3,000 teenagers in the Republic become mothers, and almost 100 per cent of these are single. Thirty years ago, the number of births to teen mothers was about the same, but only 25 per cent were single.

Rachel didn't expect to become pregnant, but she and Mark weren't using contraception. The reality of parenthood was a shock for her.

The couple never miss a meeting of the Teenage Parents Support Programme, one of three pilot projects located in Dublin, Galway and Limerick. Margaret Acton, who manages the Dublin project on behalf of Barnardos and has 80 teen mothers on her books, says teen mothers are too young to go on housing lists, so have to rear their children in their parents' overcrowded homes. They need housing tailored to their needs.

Barnardos' other goal is to keep teen mothers in school. A small budget from the Department of Education helps to fund a crèche, grinds and fees.