Bosses at the airport pledged in 2005 to install double glazing and make other improvements to minimise the din at selected schools and other community buildings lying under its flight paths.
But they had faced flak for taking so long to make good the commitment, which had its origins in a 2003 government white paper ordering airport operators to offer such measures.
When Heathrow chief executive John Holland-Kaye took up the top post in July last year, one of the first promises he made was to complete the Community Building Noise Insulation scheme by April 2015.
The airport operator announced on Tuesday (April 21) that he had kept his word, with noise insulation now completed at all 42 buildings qualifying for the voluntary initiative, 31 of which are in Hounslow.
Heathrow said the total cost of the work to the buildings, which include nursing homes and community centres as well as schools, was more than £4.8m.
Mr Holland-Kaye said: "The completion of this schools insulation programme and our innovative adobe buildings are only part of our ambitious plans to reduce the impact of aircraft noise on local communities, and be a better neighbour."
He also hailed the impact of new adobe huts being built at schools around Heathrow thanks to £1.8m funding from the airport.
The Teletubby-style huts, which are built from soil-filled tubes and offer refuge from aircraft noise during outdoor lessons, are already in place at five schools in Hounslow and Slough, with another five scheduled for completion in Hounslow this year.
Hounslow Council leader Steve Curran said: "The conclusion of the insulation programme is a good step towards creating better schools in Hounslow and we will continue to work with the airport in promoting the adobe buildings scheme and the primary and secondary school challenges, Heathrow's education programme to inspire the next generation of engineers."
Hounslow Heath Infant and Nursery School has benefited from noise insulation and the adobe huts, along with a bespoke ventilation system also funded by Heathrow.
Its headteacher Kathryn Harper-Quinn said: "We are very pleased with this noise insulation work as it makes a difference to staff and pupils, and we are just one of many schools in the Heathrow area to benefit from this scheme."
If Heathrow gets a third runway, the operator has promised to spend £700m insulating homes, schools and other buildings affected by aircraft noise - more than 20 times the £30 million currently on offer.
However, it has resisted pressure to say whether it would improve the current compensation scheme should it fail in its bid for a new landing strip.
John Stewart, chairman of the anti Heathrow expansion campaign group HACAN said: "This insulation programme has been welcomed by local people. What's important is that further insulation should not be dependent on a third runway."