Using 'behindhand' suggests a failure to meet expectations or deadlines. I'm so behindhand on my project; the teacher will be disappointed.
Pro Tip 2/3
Not Just Time
'Behindhand' can also mean delayed in progress, not only being late timewise. Despite his efforts, he was still behindhand in understanding the new topics.
Pro Tip 3/3
Social Context
In social situations, 'behindhand' can be perceived as impolite or disrespectful. He was behindhand to the dinner party, making the host anxious.