Gratton signed his first professional contract with the Millers on Tuesday, and will be available for Scarborough's upcoming fixture against Matlock Town, subject to EFL ratification.
"Jacob is highly thought of at Rotherham, he trains with the first team," said manager Darren Kelly.
"He can play anywhere along the front line and he has plenty of good attributes that he will bring with him. We would like to thank Rotherham for providing this opportunity for both parties."
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