Unions can "hire" an MP as a consultant or adviser or use one of the many lobbying organisations.
The Association of Teachers and Lecturers plays an active role in Parliamentary business. It pays MPs Ann Taylor, Labour, and James Pawsey, Conservative, Pounds 7,500 each. Liberal Democrats Don Foster and Simon Hughes share Pounds 7,500 for advising the union.
Peter Smith, ATL general secretary, said: "We pay them a retainer to provide us with information and advice on education policy. We also speak to them and others, for example on the Conservative education backbench committee, to put forward our policy."
The National Union of Teachers pays Labour MPs Gerald Steinberg and Estelle Morris Pounds 2,000 and Pounds 1,800 respectively. It also employs as advisers Labour's Win Griffiths (Pounds 1,000), Lib-Dem Don Foster (Pounds 750), and Cynog Dafis, Plaid Cymru, (who does it for free for love of the NUT).
Other bodies such as the Independent Schools Information Service are also avid lobbyists - and have access to the old boys' network.
Simon McVicar, parliamentary liaison officer for ISIS, said it was considering taking on a consultant MP. He said: "Otherwise we network very well ourselves and know everybody in the Department for Education, and it is usually quite possible to talk to ministers."
The National Association of Head Teachers pays a lobby company a retainer to pass on information and monitor Commons education debates. The union will also link up with "friendly" MPs if they are mounting a particular campaign. The Professional Association of Teachers employs Conservative MPs Sir Keith Speed and Patrick Thompson, and Labour's Lord Glenamara who is unpaid.
John Sutton, general secretary of the Secondary Heads Association, said: "We don't pay MPs a penny and we get very good value for money."