Grandma sent to Head Teacher's Study once again

Last week my granddaughter brought home a letter from school detailing three occasions last term when she was marked late at morning registration time. As we take it in turns to take Scarlett to school, we knew by the dates that these occurred on “our watch”. Mortified by the shame of it all I was prompted to write the following letter to the school. 11th January 2016, Dear Head Teacher, I refer to your letter dated 5th January 2016. Scarlett has had a word with us about our extreme tardiness on the mornings of 16th and 30th November and 14th December 2015 when we were solely responsible for providing her school transport. We humbly beg forgiveness and will endeavour to make sure there is no repeat of this behaviour. In our defence, (bearing in mind that “ignorance is no defence of the law”), we mistakenly believed: 1) Class registration was 9.00 am and not 8.55am; 2) We would be as speedy as we were on the last school run 25 years ago; 3) We might occasionally be able to park closer to the school, (perhaps there could be a petition for allocated parking for OAPs). As we are both retired now we are available for detention or any other suitable punishment deemed fit any day after school. Yours sincerely, etc. We are still awaiting suitable punishment but in the meantime I will write out 100 times “I must try harder to arrive at school on time”. Have any other grandparents been in similar trouble at school lately?