Campaigners will take part in a day of action today against controversial plans to scrap the Education Maintenance Allowance (EMA).
It comes as MPs prepare to vote on a motion, during an opposition day debate in Parliament, that calls for the Government to rethink its plans for the grant.
Ahead of this afternoon's debate, campaigners will hold a lobby in the House of Commons.
EMA teenagers from two London colleges will take part in specially-arranged lessons at Parliament during the morning, and students are to hand out "save EMA" biscuits outside Parliament.
The EMA is a weekly payment of between £10 and £30 given to the poorest 16 to 18-year-olds, living in households earning under £30,800 a year, to help them stay in education.
But the Government has announced the grant is to be withdrawn, and it is has already been closed to new applicants.
Campaigners are warning that scrapping the grant will affect thousands of youngsters who rely on the money to help fund their studies.
Sally Hunt, general secretary of the University and College Union (UCU), said the Government's decisions over the EMA have been a "complete shambles".
"First they pledged they would not axe it, now they say they will.
"They clearly have no understanding of how important the EMA is or the difference it makes to so many people's chances of improving themselves.
"Once again, they look horribly out of touch with the majority of people in the country - something highlighted by the revelation that the Education Secretary decided to axe the EMA despite never having visited a further education college."
Today's vote is "a chance for all MPs to put a stop to the mess the Government is making of the EMA and ensure they think again", she said.
Ms Hunt added: "I urge every MP to use their vote to really make a difference to the life chances of thousands of young people across the country. With the job market as it is, we cannot afford to consign a whole generation to the scrapheap of inactivity."
Martin Doel, chief executive of the Association of Colleges (AoC), said: "Given the exceptional level of public support for EMAs and the political interest in the issue - as well as the wealth of new evidence about their positive impact - it is time the Government thought again about the proposed abolition.
"While we understand the ongoing pressures on the public purse, we believe that these young people are being asked to bear a disproportionate burden."
A survey conducted by UCU with the AoC found that seven in 10 EMA recipients said they would have to drop out if their grant was withdrawn.
The UK's biggest union has warned that educational and employment opportunities for thousands of young people would be "blighted" if the allowance is scrapped.
Unite's new leader Len McCluskey said: "These plans make a sad mockery of the Government's claims that it is interested in promoting job creation and will damn hundreds of thousands of young people who will be unable to reach their full potential as citizens."
Conservative chairman of the Commons education select committee Graham Stuart told BBC Radio 4's Today programme: "The EMA goes to nearly half of all 17-18-year-olds in full-time education in the country. As few as one in ten students would not continue if it were not for the EMA.
"The Government's case is that savings have to be made somewhere and, after the orgy of spending under Labour, the Government has nothing but a diet of hard choices and this is one of them."
He said the Government was working on a replacement scheme to be administered by schools and colleges.
The Education Activist Network (EAN) said it has planned a march to start from Piccadilly at 4pm, and ending at Parliament Square where a rally will take place around 5pm.
EMA students and further education lecturers are expected to speak, according to (EAN) spokesman Mark Bergfeld.
The Metropolitan Police said officers will be handing out leaflets telling demonstrators what to expect from police during the event.
The leaflet contains information about what demonstrators can expect to see, what officers will be wearing and what to do if there is violence. It also gives information on the practice of "kettling" protesters and when it might be used.
Chief Superintendent Peter Terry, from Scotland Yard's Public Order Branch, said: "Recently we have seen many young people turn up to protest in the capital and some of them have got caught up in the disorder and violence and are now facing court with possible life-changing consequences.
"We want protesters to have a better understanding of what to expect, what the policing operation will look like on the day, and what action we could take and why, so there will be no surprises."