Bus drivers should not be allowed to refuse school children travel. This is a safety issue. At the least this can make them late at the worst they could be attacked or hurt or lost. This is unacceptable. Many children are allowed to travel on buses for free and should never be refused travel.
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My son aged 11 forgot his oyster card. He did not realise until he got on the bus. Visibly in school uniform the bus driver told him to get off the bus and said he would have to walk. Cold and dark this is a safety issue. I have witnessed countless bus drivers doing this.