Mumbai, Jan 15 (IANS) Actor-turned-director Amir Khan's directorial debut 'Taare Zameen Par' - a moving tale of a boy with learning disability - has set the box office tills ringing. It has netted Rs.770 million in its fourth week.

The movie, running neck-on-neck with last year's superhit 'Om Shanti Om' in terms of business, may even surpass the blockbuster featuring Shah Rukh Khan if it continues to sweep the box-office for a few more weeks.

Though the collections had slightly dropped in the third week of its release to hover around 60 percent, it picked up again this week. More than the media hype, it is the favourable word-of-mouth publicity that actually boosted its box-office performance.

In Mumbai, collections registered 58 percent last week. But after the Maharashtra government exempted the movie from entertainment tax (60 percent of the total ticket price), collections have climbed to 62 percent this week.

No Bollywood movie in recent memory pulled at the heartstrings of the audience - masses and celebrities alike - as 'Taare Zameen Par'.

Aamir Khan has scored over his colleague Shah Rukh Khan in content. While Shah Rukh Khan's OSO was charismatic and boasted of fresh-faced Deepika Padukone to capture the audience's imagination, Aamir touched hearts with the simplicity of the plot and sincere presentation.

Though a number of movies had been made earlier in Bollywood about physically or mentally challenged children, none came close to 'Taare...' in terms of acceptance, coupled with box-office success.

Sanjay Leela Bhansali's 'Black' (2005), based on the life of Helen Keller, was the story of a blind and deaf girl, Michelle MacNally, which was critically acclaimed at the box-office. But it failed to sparkle.

Earlier, Sunil Dutt's 1983 film 'Dard Ka Rishta', which narrated the story of a girl-child suffering from cancer, had also met the same fate though the movie launched Khushboo, the child actress who later became a successful leading lady in Tamil movies.

But comedian Mehmood's 'Kunwara Baap' (1974), about a poor rickshaw-puller adopting an abandoned illegitimate polio-afflicted child, was a box-office success.

So was the Marathi movie 'Shwaas', which was India's official Oscar entry in 2004. The story was about a boy affected by retinoblastoma, a rare retinal cancer.

The poignant tale of 'Taare Zameen Par' has left most moviegoers in tears. Watching it during a special screening in New Delhi, Bharatiya Janata Party leader L.K. Advani wept, and so did veteran director Lekh Tandon.

Tandon told IANS that he could not resist tears as he watched the movie at a suburban multiplex recently.

'Aamir has proved in 'Taare Zameen Par' that a movie sans commercial trappings, 'masala' ingredients and no heroine can also be a box-office success provided the content mix is correct. Plus, the maker must remain faithful to the script. It is Aamir's courage of conviction that runs through the movie - unobtrusively,' Tandon told IANS Tuesday.

'Taare Zameen Par' is likely to be accorded 'tax-free' status in other states as well. In view of this, PVR, the movie's world distributor, has circulated an additional 200 prints, hoping that it would continue to scale the popularity charts in the coming weeks.