Matchmaking can be a sophisticated business these days, with detailed lists of requirements systematically analysed by computer. No matter how well suited prospective partners appear, however, they sometimes simply don't get on.
It should be easier to match supply teachers with schools, where romantic sparks are not required. Yet, all over Scotland, both sides are complaining that the system is not working.
Depute headteachers spend hours with local authority lists, telephoning teachers who are already working or have moved away. Meanwhile, well qualified and willing teachers sit at home waiting for the call that never comes.
Research commissioned by the Scottish Executive recommended two years ago the establishment of a national database of supply teachers. This still seems no nearer.
Authorities continue to produce their own supply lists in isolation, as if neighbouring ones did not exist and teachers could not travel. Teachers in the central belt, at least, often live within reach of schools in half a dozen authorities.
"It is neither an efficient nor an effective system," says Bill McGregor, general secretary of the Headteachers' Association of Scotland.
"Depute heads can start phoning in the afternoon and still be at it in the evening, grinding their way down the local authority list. These are hardly ever up to date, so schools often keep their own lists of supply teachers."
This widespread practice creates problems, however, as the Scottish Executive's research report, The Management of Supply Cover in the Teaching Profession (January 2004), points out.
"When schools are unable to draw on the services of their regular supply teachers, they turn to the official system. But because so many schools are making their own arrangements, the official system is less able to work effectively," it states.
At the time of the research, there were still seven authorities that produced only paper lists. Computerised systems were being developed and used elsewhere.
Last year, Fife launched a supply teachers' messaging system which is used in all its primary schools. "We went from a paper list that was often out of date to a real-time system that has details of over 1,700 supply staff,"
says communications officer Gail Stepo. "It saves time and money and increases a school's chances of finding a supply teacher."
The system selects teachers at random, which is another advantage over a paper list arranged alphabetically: Mrs Z now gets as many job offers as Mr A, whose phone never used to stop ringing.
"It's a fairer system that allows accurate searching of staff who match the criteria," says Ms Stepo.
The system used in Midlothian is centralised but adaptable, says the director of education, Donald MacKay. "Schools phone us, whether it is far in advance or at short notice. We know if teachers are already working and we can react to any crisis - say three teachers off in one small school - by moving people around.
"There are advantages to an authority being fairly compact, but I think a system like that could operate on a larger scale.
"You do have to build in a bit of flexibility and care for schools. In particular, you want to avoid plucking teachers away who work regularly in one school and are well known to staff and pupils."
Although computerised systems introduced by authorities can be quite sophisticated, they often fail to fulfil their promise for various reasons.
Schools often fail to record their bookings; teachers on the lists of several authorities don't notify the others if they get work in one; and authorities do not update their lists often enough.
South of the border, the matchmaking role is played by commercial agencies rather than local authorities. Their systems work well because the data they contain are constantly updated, says Tish Seabourne, managing director of TimePlan, which operates throughout England and in a few Scottish authorities.
"The big difference is that in England we can deal directly with schools, which have much more autonomy. In Scotland we have to work through local authorities.
"That means we tend to provide teachers on long-term temporary contracts in Scotland, whereas in England we also do day-to-day emergency cover."
Another difference is in the time it can take to get teachers into schools because of police disclosure policies, says Ms Seabourne. "In Scotland it can take two months but we usually allow four."
It is a complaint often voiced by supply teachers themselves.
"If you register with several authorities, every one of them insists you go through Disclosure Scotland separately," says Freddie Smith, who has been supply teaching business studies for two years.
"I've missed out on work because I've been waiting for the checks to go through in one authority, while I'm already working in another.
"Also, if you leave an authority for a few months, and then go back, you have to go through it all over again. It's incredible.
"Why can't we have just one form that goes with us to different authorities?"
The duplication of paperwork that clogs up the systems does not end there, says Mr McGregor. "A retired teacher who wants to do supply teaching in another school has to go through disclosure again, as does a teacher who works part-time in one school and wants to do supply in another in the same authority.
"You can understand, though, why authorities insist on it, and why they aren't keen to let schools do their own thing with supply teachers. If one of their schools took on a teacher who had a past, they would be responsible."
All these systemic problems are exacerbated by a shortage of supply teachers. Over 40 per cent of schools surveyed three years ago, reported that suitably qualified supply teachers were "rarely available", with secondary and special schools experiencing the greatest difficulties.
These do not seem to be diminishing, says Mr McGregor. "In a lot of subjects around the country, there just aren't the supply teachers schools need. If you lose a teacher temporarily in the Western Isles, you'll be very lucky to find a replacement."
The problem is not confined to remote areas. In fact, schools in highly populated parts reported the greatest difficulty in finding supply teachers.
"This past year has been very challenging," says Lindsay Roy, the head of Inverkeithing High and a past president of the HAS.
"We were without two geography teachers for two months and two home economics teachers for three months. We couldn't get specialist supply cover in either.
"We had to go to Dublin to get a supply teacher in English.
"Colleagues around the country tell me a similar story. The Scottish Executive and Cosla (the Convention of Scottish Local Authorities) say the teachers are there. But that is not our experience."
Ian Menter, a professor of teacher education at Glasgow University and author of the 2004 report, believes little has changed since his research was published.
"Nobody has picked up on the idea of a national database," he says. "The biggest change perhaps is private agencies for providing supply teachers have begun to move into Scotland. I can see more local authorities and maybe schools turning to these agencies, but it would take a cultural shift."
A system that was up to date and capable of co-ordinating information across authorities would be a huge boon, says Mr Roy.
"It is not a good use of a senior manager's time to be phoning around for supply teachers, and it does take an inordinate amount of time. If schools could make a small financial contribution to get a high quality service, I would be happy to do so."