The tricolour was hoisted on a 110-feet high flag mast, which is 10-feet higher than the one set up by the Shimla Municipal Corporation (SMC) at the historic ridge a few months ago.
The cost of making the mast was raised through donations collected by 44 students of the school's 1991-batch, which is celebrating its silver jubilee, officials said.
Old students along with their family members were present at the unfurling of the flag on the school campus.
The band later presented the colour retreat at the school.
A soccer match between the alumni and the school team was played on the occasion.
The 157-year-old Bishop Cotton School was founded by the Bishop Edward Lynch Cotton in 1859 and its alumni include Chief Minister Virbhadra Singh, former minister Vijay Singh Mankotia and Chief Parliamentary Secretaries Rohit Thakur and Vinay Kumar.
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