Almost everyone attacks this line the same way: at full speed, immediately, and straight into the wall. There is a better method, and it is the one used by actors and broadcasters who have to get difficult copy right on the first take.
Why it defeats you
The difficulty is mechanical, not mental. The line forces rapid alternation between two sounds made in completely different ways. W is a glide produced with the lips pushed forward and rounded. Ch is an affricate produced at the roof of the mouth with the lips spread.
Would a woodchuck chuck demands that switch four times in under a second. Add vowels that are nearly identical across would, wood and could, and the brain - reaching ahead for the next word while the mouth is still finishing the last - grabs the wrong one.
Step one: break it into four
Split the line at its natural joints and treat each piece as its own exercise:
How much wood - would a woodchuck chuck - if a woodchuck - could chuck wood.
Repeat each chunk on its own until it is completely automatic. The second chunk is where nearly all failures happen, so give it twice the attention.
Step two: over-articulate at half speed
Now run the whole line at roughly half your normal speaking pace, deliberately exaggerating every w and every ch. Push the lips forward on the w. Snap the ch cleanly.
It will feel absurd. That is the point: you are teaching your mouth the full movement rather than the shortcut it will otherwise take under pressure.
Step three: add speed last
Only once the slow version is clean should you increase pace, and then in small increments. If you stumble, drop back a notch and stay there for several repetitions before climbing again.
Speed built on top of sloppy articulation always collapses at exactly the wrong moment. Speed built on top of clean articulation holds.
A few things that help
Breathe first. The full line plus the answer runs long, and people who start on an empty chest rush the end.
Keep the pitch flat. Adding melodic emphasis mid-line pulls the rhythm around and invites a stumble.
Practise the answer separately. As much wood as a woodchuck could chuck if a woodchuck could chuck wood is genuinely harder than the question, and most people never rehearse it.
Frequently asked
What is the best way to learn the woodchuck tongue twister?
Break it into four chunks - how much wood / would a woodchuck chuck / if a woodchuck / could chuck wood - and drill each separately. Then say the whole line at half speed with exaggerated articulation, and only add pace once it is completely clean.
Why is the woodchuck tongue twister so difficult?
It forces rapid alternation between the w sound, made with rounded lips, and the ch sound, made at the roof of the mouth with spread lips. The line demands that switch several times per second while the vowels in would, wood and could remain nearly identical.
Is the answer harder to say than the question?
For most people, yes. The reply packs the same consonant alternation into a longer line with fewer natural pauses, and it is rarely practised as carefully as the question.