There is something especially embarrassing about losing a pupil in rural Holland. The landscape is so relentlessly flat that it is quite a feat to lose sight of anything or anyone sticking vaguely upright. Losing one of your group on a French piste or in the Derbyshire dales is almost to be expected, but to return home having mislaid one in the Low Countries would seem a uniquely shameful thing to tell parents. And I could already imagine the headlines back home: "Gull-ible teachers: they couldn't even look after their sandwiches, let alone a group of pupils".
Sarah's absence immediately prompted young Ruth, a wheelchair-user with cerebral palsy, to summon her accompanying teaching assistant: "Come on Mrs Davis. Let's go and see if she's in the museum." Mrs Davis dutifully wheeled her there.
Upon entry to the museum - a sophisticated celebration of Dutch flood-control ingenuity - Ruth began to call out "Sarah!" at regular intervals. She instructed Mrs Davis to do the same. After a minute or so of disturbing the prevailing calm, Ruth said: "I think we'd better stop. We must look like a right couple of dicks."
A scarlet-faced Sarah soon appeared before them and concurred with that assessment.
The many light interchanges between Ruth and Mrs Davis will be my favourite memory of this trip. How inspiring the relationship between assigned teaching assistant and assisted pupil. There is so often an incomparable warmth, frankness, humour and understanding between the two. We mass-production secondary teachers can only look on with envy. Mrs Davis even calls Ruth "Andy", after the Little Britain comedy character who leaps out of his wheelchair and hurtles around outrageously whenever his naive carer looks the other way.
Although Ruth is able to walk a little, I initially thought the Andy comparison was going too far. But I soon changed my mind. Ruth positively encourages such joshing.
The only time we secondary teachers feel this deeper connection with individual pupils is, indeed, during these trips.
My other lasting memory of the Dutch trip will be of watching - while the rest were playing beach volleyball - one boy slip away to write, and shell-decorate, "I love you Dad" in the tidal sand. He told me his father had died exactly two years earlier.
After such a week of living, learning and playing as a group, you begin to question whether our current system, of each week shuffling pupils along from one specialist teacher to the next, is the right way at all.
Stephen Petty, Head of humanities at Lord Williams's School in Thame, Oxfordshire.