Headteachers must win the backing of parents rather than simply striking if they are to challenge government policies effectively and promote their own vision for schools, it has been suggested.
Government fears "the voter more than the strike", according to Russell Hobby, general secretary of the National Association of Headteachers (NAHT).
In his speech to the union's annual conference in Harrogate, Hobby warned that "industrial muscle is a blunt instrument" and should not be over-used.
He told delegates: "The hardest lesson I have learned over the last 18 months is that, to put it bluntly, we are talking to the wrong people. Traditionally, public sector trade unions have faced off - positively or negatively - towards the government. That was always going to be harder with a Conservative-led than with a Labour administration.
"The Government still holds the levers of power and of change but industrial muscle is a blunt instrument in our day and age. It is sometimes a necessary one, but the government fears the voter more than it fears the strike. Our target must be public opinion."
The NAHT took part in the TUC's day of action last November over the government's planned changes to public sector pensions.
Speaking ahead of the conference, Hobby said that the union needs to have industrial action in its repertoire, but added: "We have to have more, we have to use it (industrial action) sparingly otherwise it gets devalued."
He said there have been examples in the past in which parental support has helped heads to effect change; union moves to alter national curriculum tests were helped by the fact that parents had concerns about them and public concerns over children being taught by 68-year-old teachers also helped when winning concessions over pensions, Hobby suggested.
He also told the conference: "In this age of choice, if we have a better vision of education, we can't just deliver it, we must - for better or for worse - shout about it too. In this age of criticism of schools and the people who work in them, we need to blow our own trumpet and talk about the massive achievements we have made."
Hobby said that while a minority of parents make life difficult for schools, most pay attention to their child's education, even if they sometimes struggle to understand how the schools system works.