Data synthesis for training large reasoning models offers a scalable alternative to limited, human-curated datasets, enabling the creation of high-quality data. However, existing approaches face several challenges: (i) indiscriminate generation that ignores the solver's ability and yields low-value problems, or reliance on complex data pipelines to balance problem difficulty; and (ii) a lack of reasoning in problem generation, leading to shallow problem variants. In this paper, we develop a problem generator that reasons explicitly to plan problem directions before synthesis and adapts difficulty to the solver's ability. We recover problem-design CoT from human-authored multi-part questions, using later subquestions as targets to infer the design rationale. These traces initialize the generator, which is then optimized with a seed-conditioned reward based on solver answer consistency. The reward guides difficulty adjustment relative to each seed while favoring problems near the solver's competence boundary. Across 10 mathematical and general reasoning benchmarks, our method outperforms seed-only training by 2.69 and 3.39 percentage points after one and three rounds, respectively. The framework also extends to vision-language models. Our code is publicly available at https://github.com/WalkerWorldPeace/Reasoning-Synthesis.
Figures & tables
Fig. 1: Training pipeline for our problem generator. A reasoning model recovers problem-design CoT from paired subquestions to initialize the generator. The generator synthesizes problems from seeds, and the solver answers each problem multiple times. Majority-answer consistency provides the feedback used to compute the seed-conditioned training reward.
Fig. 2: Recover the latent problem-construction logic from paired sub-questions, using the earlier one to infer a rationale for designing the follow-up.
MATH
GSM8K
AMC
Minerva
Olympiad
AIME24
AIME25
Avg.
Qwen3-4B-Base
Base Model
66.40
70.49
44.68
17.71
31.01
9.38
7.22
35.27
Seed Set
79.60
92.79
56.35
31.73
39.76
14.52
12.02
46.68
Self-Instruct [ 56 ]
77.40
92.79
55.49
32.84
37.69
12.17
7.40
45.11
+ CoT-Self-Instruct [ 24 ]
78.20
93.47
56.00
32.47
38.58
11.94
7.04
45.39
+ RLMT [ 40 ]
79.60
91.05
55.80
31.25
39.26
13.62
10.36
45.85
TABLE I: Performance Comparison on Mathematical Reasoning Benchmarks. Pass@1 accuracy (%). AMC, AIME24, and AIME25 use the mean of 128 samples per problem (avg@128). Indented rows are variants of the method above (Sec. V-A3 ). Bold and underlined values are the best and second-best scores.
Super GPQA
BBEH
MMLU- Pro
Avg.
Qwen3-4B-Base
Base Model
20.88
7.57
37.38
21.94
Seed Set
29.74
11.22
52.88
31.28
Self-Instruct
30.07
11.13
56.79
32.66
+ CoT-Self-Instruct
30.35
11.50
57.86
33.24
+ R-Zero
31.27
11.19
58.79
33.75
TABLE II: Performance Comparison on General-Domain Reasoning Benchmarks
Math Vista
Math Vision
Math Verse
Avg.
Qwen2.5-VL-7B-Instruct
Base Model
68.40
23.35
43.53
45.09
Seed Set
69.00
29.28
45.23
47.84
Self-Instruct [ 56 ]
69.80
29.60
46.40
48.60
+ CoT-Self-Instruct [ 24 ]
69.30
27.63
45.58
47.50
+ R-Zero [ 38 ]
69.30
26.64
44.72
46.89
TABLE III: Performance Comparison on Multimodal Reasoning Benchmarks
MATH
GSM8K
AMC
Minerva
Olympiad
AIME24
AIME25
Avg.
Qwen3-4B-Base
Base Model
66.40
70.49
44.68
17.71
31.01
9.38
7.22
35.27
Seed Set
79.60
92.79
56.35
31.73
39.76
14.52
12.02
46.68
Self-Instruct [ 56 ]
79.60
92.57
55.16
31.99
38.07
14.53
13.96
46.55
+ CoT-Self-Instruct [ 24 ]
78.60
93.63
55.53
33.82
37.04
10.78
11.04
45.78
+ R-Zero [ 38 ]
80.80
92.80
60.00
30.51
44.44
17.29
14.79
48.66
TABLE IV: Controlled Comparison with a Fixed Training-Set Size. Pass@1 accuracy (%), with avg@128 on AMC, AIME24, and AIME25. Each method uses the same 4,000 seeds plus 4,000 retained synthetic problems. Indented rows are variants of the method above (Sec. V-A3 ). Bold and underlined values are the best and second-best scores.
Method
Comparison setting
Avg. (%)
MetaMath
Seed-conditioned rewriting
46.80
ScaleDiff
Released-data utility
47.30
Ours
Seed-conditioned generation
49.90
TABLE V: Comparison with Mathematical Data Synthesis. Macro-average accuracy over seven mathematical benchmarks with the same solver and training-set size.
Reward variant
Avg.
Boundary only (R-Zero)
45.17
Inversion only
47.61
Full reward (Ours)
49.24
TABLE VI: Reward Ablation on Seven Mathematical Benchmarks
Fig. 3: Contour density plot of solver consistency and accuracy on MATH. The dashed red line shows the best-fit linear regression, and the yellow dotted line denotes the identity reference ( y=x ). Pearson r=0.887 indicates a strong positive relationship.
Checkpoint
Pearson r
Spearman ρ
Confidently wrong (%)
Invalid / unsolvable (%)
Parseable answers (%)
Step 0
0.78
0.81
2.1
6.4
86
Step 5
0.74
0.79
2.6
7.1
85
Step 10
0.76
0.80
2.4
6.8
84
Step 20
0.73
0.77
2.9
7.5
83
TABLE VII: Reliability of Solver Consistency during Generator RL. Confidently wrong denotes consistency ≥0.8 with a majority answer that does not match the verifier’s reference answer. Parseable answers are responses with an extractable final answer.
Fig. 4: Training dynamics across iterations : the problem generator’s reward score, flip success rates for the original and new problems, and changes in difficulty for the original and new problems.
Fig. 5: Case study under high solver feedback: increased difficulty. Responses to the line-intersection problem.
Method
Well-posed ↑
Solvable ↑
Ambiguous ↓
Seed near- duplicate ↓
Strategy changed ↑
Label–verifier agreement ↑
CoT-Self-Instruct
82
80
8
21
19
83
R-Zero
79
76
9
18
22
81
Ours
86
84
5
4
31
88
TABLE VIII: Quality Audit of Generated Problems. All values are percentages. Each method contributes 100 candidate problems sampled from the same seed pool.
Labeler pair
Retention agreement
Answer agreement
o3-mini vs. DeepSeek Pro
80.0
71.9
o3-mini vs. DeepSeek Flash
79.3
74.5
DeepSeek Pro vs. DeepSeek Flash
87.3
91.8
TABLE IX: Agreement between Labeling Models. All values are percentages on the same generated problems. Retention agreement compares decisions to retain or discard a problem; answer agreement compares normalized final answers.
MATH
GSM8K
AMC
Minerva
Olympiad
AIME24
AIME25
Avg.
Qwen3-4B-Base
MATH Seed Set
79.60
92.79
56.35
31.73
39.76
14.52
12.02
46.68
MATH Augmentation
82.00
92.87
60.52
32.84
44.36
17.44
14.65
49.24 (+2.56 pp)
GSM8K Seed Set
79.60
92.72
54.93
32.47
38.28
13.16
11.03
46.03
GSM8K Augmentation
78.40
93.55
59.38
32.10
41.84
13.14
13.71
47.45 (+1.42 pp)
DAPO Seed Set
76.00
91.88
53.82
29.52
36.94
9.78
6.80
43.53
TABLE X: Generalization across Different Seed Sets. “Seed Set” trains the solver on the original sampled problems only. “Augmentation” expands the seed set with synthetic problems generated by our MATH-trained generator. We report pass@1 accuracy (%) on the seven mathematical reasoning benchmarks.
Fig. 6: Performance comparison across iterations on all ten benchmarks. The solver improves as the generator and solver are trained alternately.
Appendix figures & tables1 asset
Supplementary material from the paper’s appendix.
Appendix
MATH
GSM8K
AMC
Minerva
Olympiad
AIME24
AIME25
SuperGPQA
BBEH
MMLU-Pro
Avg.
Qwen3-4B-Base
Iteration 1
82.00
92.87
60.52
32.84
44.36
17.44
14.65
31.33
11.35
60.11
44.75
Iteration 2
81.60
92.56
64.29
34.69
45.25
17.00
14.65
31.90
11.81
59.52
45.33
Iteration 3
82.40
93.25
64.65
32.10
44.51
18.67
15.04
31.86
12.27
59.73
45.45
Appendix
TABLE XI: Performance across Co-evolutionary Iterations on Ten Benchmarks. These scores correspond to the radar chart in Fig. 6 . The generator and solver are trained alternately in successive rounds.