/usr/lib/education-tasks/edu-tasksel-setup is in education-tasks 1.812+deb8u1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | #!/bin/sh
error() {
    print "error: " $@ 1>&2
}
setup_tasksel_overrides() {
    # Modify tasksels desktop test so the normal Debian desktop
    # profiles are not installed. Use dpkg-divert to to switch to our
    # version
    sed -e 's/if desktop_hardware/# Do not install a desktop - added by debian-edu-install\nunmark\n\n&/' \
        < /usr/lib/tasksel/tests/desktop \
        > /usr/lib/tasksel/tests/desktop.edu
    chmod 755 /usr/lib/tasksel/tests/desktop.edu
    dpkg-divert --package debian-edu-install --rename --quiet \
        --add /usr/lib/tasksel/tests/desktop
    ln -sf ./desktop.edu /usr/lib/tasksel/tests/desktop
    # And for the standard system task too
    sed -e 's/^case/# Do not install standard system task - added by debian-edu-install\nexit 3\n\n&/' \
        < /usr/lib/tasksel/tests/new-install \
        > /usr/lib/tasksel/tests/new-install.edu
    chmod 755 /usr/lib/tasksel/tests/new-install.edu
    dpkg-divert --package debian-edu-install --rename --quiet \
        --add /usr/lib/tasksel/tests/new-install
    ln -sf ./new-install.edu /usr/lib/tasksel/tests/new-install
}
remove_tasksel_overrides() {
    for test in desktop new-install ; do
        file=/usr/lib/tasksel/tests/$test
        if [ -x $file.edu ] ; then
            rm $file
            dpkg-divert --package debian-edu-install \
                --rename --quiet --remove $file
            rm $file.edu
        else
            error "Missing divert for $file."
        fi
    done
}
case "$1" in
    setup)
	setup_tasksel_overrides
	;;
    teardown)
	remove_tasksel_overrides
	;;
    tasksel)
	setup_tasksel_overrides
	shift
	tasksel $@
	remove_tasksel_overrides
esac
 |