The Queen has urged Commonwealth leaders to use the "optimism and enthusiasm" of young people as a resource to help solve world problems.
The Queen watched a cultural show depicting the history of Uganda
She spoke at the opening of the Commonwealth Heads of Government Meeting (Chogm) during her state visit to the Ugandan capital, Kampala.
The 50 leaders at the gathering represent two billion people globally.
Her comments came as Pakistan was suspended from the Commonwealth "pending restoration of democracy".
'Respect and rights'
For the first time Prince Charles also attended the Chogm.
Prior to the conference he toured one of Kampala's most impoverished districts and met former prostitutes who are being trained for legitimate work by a UK charity.
The Queen also spent time visiting other parts of the city.
On Thursday she toured an Aids clinic and shook hands with a HIV patient in public for the first time.
At the start of the three-day conference the Queen told delegates that a youth forum event held earlier in the week revealed people with a virtually boundless optimism and enthusiasm.
She said: "This is an energy that should be tapped more fully.
"Young people can and should play a part in the many global challenges that cannot be resolved by older generations alone, whether in the Commonwealth as a whole or in each of its member countries."
The Queen commended the gathered heads of government for their universal commitment to "respect for fundamental human rights".
She said: "The theme chosen for this Chogm, Transforming Societies, conveys a clear commitment to change for the better.
"No single society has achieved perfection, and there is no single recipe for success.
"No one could expect that. But we do know that giving people the greatest possible voice in the way they are governed, and the greatest possible access to education, are two of the most important ingredients."
Ugandan President Yoweri Museveni said the Commonwealth could help countries to transform their economies and way of life.
He told the gathering it was the duty of each nation to transform the lives of their rural poor.
President Museveni said: "You cannot, for instance, sustainably protect the environment if the majority of the people are still in primitive agriculture leading to the encroachment of forest reserves.
"Or if people are still using the biomass for cooking because they do not have electricity."
The organisation's outgoing secretary-general, New Zealander Don McKinnon, echoed the sentiments of the Queen.
He said: "[It] is young people - so often voiceless - who make up nearly half our number.
"Without them at the core of our planning, our budgeting and our doing, our Commonwealth has no future."
Prime Minister Gordon Brown, who also attended the meeting, used it as an opportunity to send out a message to Pakistan's President Pervez Musharraf who has declared a state of emergency and called off elections.
He told delegates: "President Musharraf has said that he will take steps necessary to restore democracy.
"The Commonwealth is strongly of the view that he must now do so.
"We will work with Pakistan and the Commonwealth to ensure Pakistan returns to its rightful position in the Commonwealth once the remaining steps are taken."
Pakistan said its suspension from the Commonwealth because of the imposition of emergency rule was "unreasonable and unjustified".
The Commonwealth had failed to appreciate Pakistan's "serious internal crisis", the foreign ministry said.